If you are using the next generation of Google Analytics, (Google officially made Google Analytics 4 "GA4" the default option for all new Analytics properties in October 2020), you'll need to add the GA4 Tag to your PMP site to allow Google Analytics 4 to collect relevant data.
To add the GA4 Tag to your new website, follow these steps:
1.) Follow the instructions for the Global Site Tag (gtag.js) here - https://support.google.com/analytics/answer/9304153?hl=en#zippy=%2Cadd-the-global-site-tag-directly-to-your-web-pages to get the code that needs adding in the <head> section of your PMP website.
2.) Once you have this code, you can add it to Website Basics > Code
Instructions on how to do this can be found here: https://promotemyplace.zendesk.com/hc/en-us/articles/216230643-How-to-add-code-such-as-tracking-code-to-your-website
Please note: If you already have an existing PMP website with the original Analytics already added, you can use both the original Google Analytics and the new GA4.
Don't remove the old analytics.js tag; it will continue to collect data for your Universal Analytics property. The gtag.js tag that you're adding will collect data for your new Google Analytics 4 property.
More information about using the original Google Analytics and GA4 can be found here: https://support.google.com/analytics/answer/9744165?hl=en-GB&utm_id=ad#use_existing_tags&zippy=%2Cadd-your-tag-directly-to-your-web-pages